\defineblank[aroundfloat][0.8\lineheight plus 3fill minus 0.2\lineheight]
\setupwhitespace[0pt plus 1fill]
\letprependtoks \stoptextO=vfilll \stoptext\def\stoptext{\vfilllto \stoptextO}everystoptext
\def\Par{bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla}